1. Field of the Invention
The present invention relates to a switch for detecting a rotational position, such as an inhibitor switch for electrically detecting a shift point of an automatic transmission, and a welding method of the switch.
2. Description of Related Art
Examples of inhibitor switches in accordance with related art are shown in cross sectional views of FIG. 5. As shown in FIG. 5, an inhibitor switch 101 is composed of a terminal block 103, a cover 105, and a moving block 107.
The terminal block 103 has a plurality of fixed contact points 109. The terminal block 103 is coupled with the cover 105 to form a switch housing 111. A contact accommodating chamber 113 is formed inside the switch housing 111. The terminal block 103 and the cover 105 are coupled in a thermal welding part 115 by, for example, ultrasonic welding.
In the thermal welding part 115, a share joint is used to ensure high welding strength. The share joint allows a circular projecting rim 119 on the side of the cover 105 to be guidably fitted all around a circular welding groove 117 on the side of the terminal block 103 at the corresponding portion of the thermal welding part 115 before thermally welded, so that the axial centers of the terminal block 103 and the cover 105 may be aligned and the axial rotation direction thereof may be positioned around the axis of the moving block 107. The terminal block 103 and the cover 105 are vibrated by means of ultrasonic waves while being pressed against each other at this positioning state. As a result, the projecting rim 119 and the welding groove 117 are thermally welded, achieving reliable ultrasonic welding.
However, at the time of aligning the terminal block 103 with the cover 105 during the ultrasonic welding process, the projecting rib 119 is required to be guided and fitted in the welding groove 117 on the entire circumference of the switch housing 111. Therefore, due to influences of a position accuracy between the welding groove 117 and the rib 119, a configuration accuracy thereof and the ultrasonic vibration, each of the terminal block 103 and the cover 105 possibly causes the alignment deviation from the axis center of the moving block 107 at a welding state. When the alignment deviation occurs, it raises the problem that the detection accuracy of the switch may deteriorate (refer to JP2002-192617A).
As described above, the conventional switch has the following problem. Since the ultrasonic welding is performed in a state where the rib is guided and fitted in the welding groove, the alignment deviation tends to occur due to influences of a position accuracy between the welding groove 117 and the rib 119, a configuration accuracy thereof and the ultrasonic vibration.
In view of the above, there exists a need for a switch and a welding method of the switch which overcome the above mentioned problems in the conventional art. The present invention addresses this need in the conventional art as well as other needs, which will become apparent to those skilled in the art from this disclosure.